All dental resins in current usuage are hindered by polymerization shrinkage which creates stress states (tensile) within the set material. This eventually leads to dimensional changes or microcracking and, as a result, composites lose strength and abrasion resistance and have open margins, while dental adhesives are lost from enamel surfaces and dentures distort and become ill fitting. Resin based die materials are always undersized. Elimination of polymerization shrinkage or creation of polymerization expansion would have far reaching results in dentistry. We have synthesized in these laboratories unsaturated spiro ortho carbonate (SOC) monomers which have polmerization expansions of up to 8 percent. These monomers react by free radical mechanisms as used in dental resin systems. SOC monomers can be made to copolymerize with dimethacrylate adducts. The resulting highly cross-linked structures exhibit polymerization expansion and excellent strength. When implanted, SOC based polymers exhibit a mild inflammatory response similar to current dental composite resins. The specific objectives of this research proposal are: (1) Optimize comonomer formulations (utilizing SOCs) and free radical catalyst systems to yield high strength composites with controlled degrees of polymerization expansion; (2) Evaluate adhesive formulations based upon expanding monomer additions via physical testing employing thermal cycling; (3) Synthesize additional candidate monomers, both saturated and unsaturated; (4) Evaluate the use of cationic catalysts, in particular stannic fluoride, for these ring opening polymerizations where, after polymerizations, fluoride could slowly leach from the structure. All formulations will be screened for dental use based upon strength, hardness, adhesion to enamel, abrasion resistance, internal stress state by magnetostrictive transducers, and in particular, toxicity.